The present invention relates to reduction of hydrocarbon and nitrogen oxide engine emissions, and more particularly relates to an integrated fuel reformer-engine system and method for providing low hydrocarbon and nitrogen oxide emissions in internal combustion engines over a range of operating conditions.
Atmospheric pollution generated by exhaust emissions from conventional gasoline and diesel powered internal combustion engines has caused both federal and state governments to enact laws and establish regulations which impose ever greater restrictions on the performance of motor vehicles in the areas of exhaust gas emission and fuel economy. For example, California Ultra Low Emission Vehicle (ULEV II) emissions standards include a Super Ultra Low Emission Vehicle (SULEV) emissions standard. In normal, light load, summer operating conditions represented by the U.S. FTP (United States Federal Test Procedure), a vehicle developed and certified to the SULEV level emits extraordinarily low emissions. Gasoline-fueled vehicles that robustly meet SULEV standards over their useful lives (and under real-world conditions) would offer a significant step toward eliminating the automobile as a source of regulated pollutants.
Vehicles operating on hydrogen-enriched fuels are attractive as low-emissions vehicles. Hydrogen-enriched fuels can be produced from a variety of sources, including gasoline. And hydrogen-enriched fuels have several attributes enabling near-zero vehicle emissions, including: a fuel source that contains no hydrocarbons for near-zero hydrocarbon emissions; the ability to promote rapid catalyst heating to improve exhaust catalyst light-off; and the ability to operate under ultra-lean/high EGR conditions to greatly reduce NOx emissions.
Hydrogen fuel can be dispensed to the vehicle and stored on-board, or hydrogen can be produced on-board the vehicle with an on-board reformer. Currently, sufficient infrastructure is lacking for widespread use of vehicles with hydrogen stored on-board, and significant technical challenges remain to provide an attractive on-board storage method. With on-board reforming, hydrogen enriched fuel can be produced from gasoline (as well as other liquid or gaseous fuels). On-board reforming of gasoline generally requires reaction temperatures of roughly 600xc2x0 C. to 900xc2x0 C. typically in the presence of a catalyst, to ensure that the reactions provide high hydrogen yields and inhibit the formation of soot. The gasoline itself provides the necessary energy to reach the steady-state reaction temperature requirements.
What is needed in the art is a system that is capable of robustly meeting SULEV emissions criteria over the range of real-world operating conditions. What is further needed in the art is a system and method that enables reduction of hydrogen and nitrogen oxide (NOx) emissions to near zero at cold start through to periods of vehicle road loads. What is further needed in the art is a system and method for reducing exhaust emissions while providing fuel economy and overall engine efficiency. What is further needed is such a low emissions system that can be adapted to a variety of vehicle types, including larger, higher emitting vehicles, such as those employing diesel engines.
The present invention provides a low-emissions integrated fuel reformer-engine system and method. In one embodiment, the present system and method provide near-zero cold start hydrocarbon and NOx emissions with ultra-lean start using substantially 100% reformate fueling. In another embodiment, the present system and method provide accelerated catalyst heating using reformate supplied to the exhaust. In another embodiment, the present system and method provide ultra-low NOx emissions at light and mid loads using extreme dilution (lean fuel or exhaust gas recirculation) and partial reformate fueling.
The present system comprises an on-board fuel reformer for receiving a supply of hydrogen-containing liquid fuel, such as gasoline, and a supply of air and converting the same into a hydrogen-rich reformate fuel; an engine having a reformate intake, a liquid fuel intake, an air intake, and an exhaust outlet; an exhaust catalyst having an intake for receiving engine exhaust, reformate, or a combination thereof, and an outlet for discharging engine exhaust after treatment. Control means meter the supply of air and fuel intake in the form of reformate alone or a blend of liquid fuel and reformate supplied to the engine, and the supply of reformate to the exhaust catalyst so as to provide low hydrocarbon and NOx emissions over a range of operating conditions from cold-start to vehicle road-loads. The control means is configured to provide low emissions in combination with optimized fuel economy and system efficiency. In an alternate embodiment, a small supply of reformate, such as bottled reformate gas, is stored on-board for use during warm-up of the on-board reformer or other periods when the on-board-reformer is not operational.
The present method comprises producing hydrogen-rich reformate fuel with an on-board fuel reformer, fueling the engine with reformate, a liquid fuel, or a combination thereof, and treating the engine exhaust, reformate, or a combination thereof, in the exhaust catalyst. The method comprises controlling the supply of one or a combination of reformate, liquid fuel, and air to the engine and exhaust catalyst to achieve low hydrocarbon and NOx emissions over a range of engine operating conditions including cold-start, idle, and road-loads.
In a preferred embodiment, accelerated catalyst heating is employed to rapidly bring the exhaust catalyst up to operating temperature. In one embodiment, accelerated catalyst heating is by supplying reformate or a mixture of reformate and engine exhaust to the exhaust catalyst for a time sufficient to warm the exhaust catalyst to operational temperature. In another embodiment, accelerated catalyst heating comprises igniting the engine exhaust with an ignition source disposed between the engine exhaust outlet and the exhaust catalyst and heating said exhaust catalyst therewith.
The present reformer-based system uses on-board partial oxidation fuel reforming (POx) in combination with catalytic after-treatment of exhaust to provide near-zero engine-out emissions over a range of operating conditions including cold-start. Further, the present system is adaptable to a broad spectrum of engines and vehicles. Efficient fuel reforming further enables both very low emissions and improved fuel economy. The present system allows reduced precious metal loading rates to the catalyst over prior systems and allows the catalyst to be located further downstream in the exhaust (for a less harsh environment) than after-treatment-based SULEV systems. The present system further provides near-zero cold start emissions even with poor volatility fuels and at very cold ambient temperatures.